The present invention relates to a signal processing method for use with a data recorder, for example.
When data supplied from a host apparatus, such as a host computer or the like, is recorded on and reproduced from a magnetic recording apparatus, such as a data recorder or the like, there has hitherto been used a signal processing apparatus in which data that had been converted in accordance with a predetermined logical format is recorded on the magnetic recording apparatus upon recording and data that had been reproduced from the magnetic recording apparatus is reconverted into original data in accordance with the predetermined logical format upon reproduction.
A recording apparatus using a magnetic tape is used as a computer peripheral equipment. Having been compared with a direct access device such as a magnetic disc in which data at an arbitrary position can be accessed randomly, a magnetic tape is what might be called a sequential access device because data recorded therein is accessed sequentially.
A sequential access device of the computer systems implements a file formatting on the tape to thereby form a tape mark for segmenting files and an end mark by recording consecutive two tape marks after the last file. Moreover, a directory information table (DIT) which comprises address data indicating the position of the tape mark on the tape, volume management information for managing a tape medium itself, such as a tape reel, a tape cassette or the like and update information are recorded on the tape.
FIG. 1 of the accompanying drawings shows a physical beginning of tape position PBOT, a logical beginning of tape position LBOT, a physical end of tape position PEOT and a logical end of tape position LEOT which will be referred to hereinafter simply as "position PBOT", "position LBOT", "position PEOT" and "position LEOT", respectively.
As shown in FIG. 1, in addition to a helical track HT where file data, the directory information table DIT and tape marks TM are recorded, there are a control track CT on which servo information and address information are recorded by a stationary head in the longitudinal direction of the tape and annotation tracks AT1, AT2 on which memo information or the like is recorded by a stationary head in the longitudinal direction of the tape. The track formed in the longitudinal direction is used for recording area for audio time code when the tape is used as a medium for recording a video signal.
As shown in FIG. 2, on the helical track HT are recorded file X as file data, the directory information table DIT and the tape marks TM. Further, on the helical track HT is recorded sub code SC in which track attribute data serving as information to discriminate the type of track is coded.
As shown in FIG. 3, the sub code SC of a directory information table track DITT has a value of "AAA", the sub code SC of a tape mark track TMT has a value of "BBB", the sub code SC of a user data track UDT has a value of "CCC", and the sub code SC of a dummy track DT has a value of "DDD".
The user data track UDT is a track in which user data is recorded in the file as valid data in actual practice. The dummy track DT is a track in which useless data that had been entered because of the device circumstance is recorded as invalid data.
When the tape that is used as the sequential device of the computer system is unloaded from the driver, in order to protect the tape from being damaged, the tape is not unloaded from the driver until the tape is rewound to the position PBOT. Also, when the tape is loaded on the driver, data is not written in or read out from the tape until the tape is rewound to the position PBOT.
Accordingly, the directory information table DIT in which the address data indicating the position of the tape mark on the tape, the volume management information for managing the data of the tape medium itself, such as tape reel, tape cassette or the like and the update information are recorded is provided at the tape top, i.e., at the position substantially next to the position LBOT.
However, if a file is sequentially made, then the above-mentioned signal processing method records the directory information table DIT as the updated management information each time the file is made. Therefore, the tape should be rewound to the position PBOT in order to record the directory information table DIT, which unavoidably needs a lot of time. Furthermore, the magnetic tape is very frequently traveled near the tape position in which the directory information table DIT is recorded. There is then the disadvantage that the tape itself tends to be damaged.
To solve this problem, the updated directory information table DIT is temporarily stored in some suitable means, such as a semiconductor memory or the like, and the directory information table DIT that had been stored in the semiconductor memory is transferred to the tape after the tape was rewound to the position PBOT immediately before the tape is changed. This method also causes the following problem. That is, the memorized content of the semiconductor memory is erased when a power supply is disabled so that the preserved state of the directory information table DIT becomes unstable as compared with the tape.
Although a nonvolatile memory is considered as means for preventing the memorized content of the memory from being erased when an electricity failure occurs, the nonvolatile memory is limited in number to write therein data and is not practical in use for this reason. Furthermore, when the power supply is disabled to erase the directory information table DIT before the updated directory information table DIT is transferred to the tape, the files should sequentially be read out from the position PBOT to the last file of the tape and the directory information table DIT should be reconfigured. There is then the disadvantage that the signal processing becomes complex and needs plenty of time.